CP shared-KV slot remaps already have forward-batch lifetime, but the IPC materialize path rebuilt owner/source/dense descriptor tensors on every layer. Cache prefix/current IPC descriptors on the token and paged slot-remap objects, keyed by layout, spans, device, descriptor kind, and prefix capacity, so all model layers can reuse the same request/batch-plan descriptors.
Constraint: Small-extend cache-hit workloads showed descriptor setup could exceed the all-reduce baseline before any IPC kernel work ran.
Rejected: Global descriptor cache | slot-remap lifetime is safer and avoids stale entries across request/batch-plan changes.
Rejected: Cache without physical page capacity | prefix descriptors encode capacity-invalid pages and must miss when capacity changes.
Confidence: high
Scope-risk: moderate
Directive: Do not reuse descriptors across different slot_logical_pages identity, CP layout, spans, device, or prefix capacity; stale descriptors can alias dense slots across requests.
Tested: Local py_compile; local git diff --check; remote g0034 cjy-glm5-new targeted descriptor tests 2 passed; remote full test_cp_shared_kv_runtime.py 146 passed, 21 warnings, 2 subtests passed.
Not-tested: Full ETE throughput/accuracy after descriptor cache; CUDA service benchmark still needed to quantify speedup.
(cherry picked from commit addd1ca1571e41458315d15304a0e841682fe8fa)
cd4412a4b8